高寒草甸地下根系生长动态对积雪变化的响应

2013年11月至2014年8月在青藏高原东缘红原县高寒草甸通过人工堆积的方法,进行了积雪量野外控制试验。以自然降雪的积雪量为对照(CK),设置了S1、S2和S3(积雪量分别为自然对照的2倍、3倍和4倍)3个处理,运用微根窗法追踪研究了积雪量改变后高寒草甸植被根系生长动态,并测定了积雪变化对土壤温度的影响。结果表明:高寒草甸植被根系生长存在明显的季节性变化,随着时间的推移,根系表面积、根尖数量及现存量逐渐增加并在8—9月达到最大值;当冬季积雪量达到143.4mm(S1),对根系生长最为有利(根系表面积、根尖数量、现存量及生产量最大),根系生长旺盛期(净生产速率较高)有所提前和延长,但随着积雪量进一步增加,积雪对根系生长的正效应逐渐降低,根系生长旺盛期逐渐推迟甚至消失;研究还发现,随着积雪量增加,0—10 cm土层土壤温度逐渐降低,相似的变化规律也出现在10—20 cm土层,但在时间上有所延迟;相关性分析表明,在不同土层中,根系生长与土壤温度均呈正相关。因此,积雪变化通过改变土壤温度影响高寒草甸植物根系的生长发育,最终可能会影响高寒草甸生态系统的碳分配与碳循环过程。

Response of belowground root growth dynamics to snow cover change in alpine meadow

Permanent or seasonal snow cover is widespread on the Tibetan Plateau. Seasonal snow cover, which is affected by global climate change, is dominant in the northwestern part of Sichuan Province, on the eastern edge of the Tibetan Plateau. The root system is sensitive to environmental change. The effects of seasonal snow accumulation and thawing on soil physicochemical properties and microorganisms change could influence the root system in alpine meadow. Understanding the environmental effect on the root system of alpine meadow is essential to better understand the response mechanisms of terrestrial ecosystems to global climate change. From November 2013 to August 2014, we conducted the field study on controlled snow cover gradients in an alpine meadow of northwestern Sichuan. Four snow cover gradients were established: natural snowpack (control), and snowpack manipulated to be 2-, 3-, and 4-folds that of control. The root growth dynamics of plant communities and their responses to snow cover gradients were continuously monitored using the Minirhizotron method. The effects of the snow cover gradients on soil temperature were also measured. The results showed that soil temperature decreased with increasing snowpack volume. The optimum root system growth was observed with the natural snowpack. The root growth period was lower in the doubled natural snowpack compared with other treatments at the beginning, but the final root growth of was faster than that of the control. Belowground root system growth was restricted in the tripled snowpack. Correlation analysis showed that the root growth was positively correlated with soil temperature. Our results indicate that the winter snowpack change directly impacts subsurface ice storage, which in turn affects hydrothermal regimes in the alpine meadow soil and thus root system growth. Belowground root systems may suffer damage when the melt water refreezes underground after infiltrating into the soil and undergoes subsequent freeze-thaw cycles. Overall, moderately increased snowfall is conducive to the growth of the belowground root system, but excessive snow inhibits the belowground root system. Therefore, change in winter snowpack could alter carbon distribution and the carbon cycle in alpine meadow ecosystem.